


Birthday Shenanigans

by Deku_Lily



Category: Quantumtale-Au, Undertale (Video Game)
Genre: Alternate Universe, Bad Puns, Birthday Fluff, Birthday Traditions, Home Invasion, Minor Injuries, TK broods a little, TK gets a booster shot and doesn't like it, TK runs a lot
Language: English
Status: Completed
Published: 2018-09-29
Updated: 2018-09-29
Packaged: 2019-07-18 21:43:56
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,438
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16127342
Author URL: https://archiveofourown.org/users/Deku_Lily/pseuds/Deku_Lily
Summary: Undyne has just learned about a human birthday tradition and wants to try it on TK for good luck, which he's not too keen on. He runs for his life and shenanigans ensue.





	Birthday Shenanigans

**Author's Note:**

> This is just a little fanfic I wrote back in May to celebrate TK!Sans’ birthday, PerfectShadow06’s Undertale AU kiddo (my first written gift to anyone, ever). It was also to thank her for bringing such an adorable skelly into our lives. ^w^ It was originally just on Tumblr, but now I've gone and brought it here. So here we go! XD
> 
> TK!Sans and all the other Time Kids/the QuantumTale gang are [PerfectShadow06’s](https://perfectshadow06.tumblr.com) babies. I’m just writing about them for kicks and (hopefully) laughs. :3

 

 

* * *

 

 

It was a nice day out. The birds were singing, the flowers were blooming… A young skeleton known outside of his universe as “TK” lounged beneath his favorite napping tree, staring up at the sky through its leaves. However, he wasn’t napping, this time. Today, he was thinking.

 

TK Sans possessed unique abilities, allowing him to travel to other worlds and their varied timelines. In them, he met other versions of himself. Almost all of them were older than him, and that made him wonder. Was he one of them, in the making? If so, which one would he be? Was that something he could decide, or would Fate ultimately decide that for him?

 

He hoped Fate stayed out of it. Some of those other Sanses were pretty ticking weird, when they weren’t total goobers or just plain insane…

 

His thoughts were interrupted when Undyne stomped up to him and, without any preamble, boldly said, “YO, nerd punk!! How old are you?”

 

Sans sat up, raising a brow ridge at her as he asked, “why d’you wanna know?”

 

Undyne rolled her eyes impatiently. “Because Papyrus told me it was your birthday, today! And there’s this human tradition I heard about, that I want to try. But it depends on how old you are, so just tell me, already!”

 

Sans didn’t immediately answer. He hadn’t realized it was his birthday, already. But leave it to good ol’ Papyrus to remember, for him. Sans couldn’t help but chuckle at how cool his baby bro could be. Finally, he said to Undyne, “before i tell you, what’s this tradition you heard about?”

 

She grinned before telling him, giving him a _really_ bad feeling.

 

“It’s a good luck tradition, where the birthday boy (or girl, I guess) gets spanked once for every year they’ve lived, plus one. And guess who gets to try it out today?” She cracked her knuckles with a smile that did NOT bode well for Sans.

 

The skeleton sat upon the ground for a second, blinking at his friend. Then he calmly stood, brushed himself off, looked her straight in the eyes and said “no tickin’ way,” before running for his life. He heard her roaring behind him.

 

“ _NGAAHH!_ GET BACK HERE, YOU BONY COWARD!!!” Sans didn’t dare look back, but he _knew_ she was gaining on him.

 

* _not good!_ The young skeleton reached into the bag of tricks he kept on hand for emergencies like this. Finding what he was looking for, he chucked a special little surprise behind him. Undyne was stopped by a cloud of smoke and confetti, letting him slip away. She wasn’t going to be happy with that, but if it got Sans away from the spearfish hunting for him, it was all good to him.

 

~~~~~***~~~~~***~~~~~***~~~~~

 

He decided to hide in the lab, for a while. Upon entering, Sans tip-toed his way around all the bits and pieces scattered on the floor. It looked like Alphys was working on her latest pet project (that, or it blew up. Again.)

 

Suddenly, one of his shoelaces caught on something, tripping him! His arms windmilled as he fell chin-first into a box full of miscellaneous parts. He heard Alphys’ surprised voice as he struggled to heave himself out of the box, his legs kicking in the air and unable to find any purchase.

 

“Oh my god! S-Sans? Are y-you alright? I-I didn’t hear you come in…” Finally, she got over her shock and pulled him out by the back of his coat. A couple of gears were stuck in his eye sockets… Sans grinned at her, pointing at his face.

 

“oh, you know me. just **gearing** up for my next big adventure!”

 

Alphys didn’t laugh, but she _did_ take the gears out for him, letting Sans see her unamused expression. It still made him chuckle.

 

“If you can joke around like that,” said the budding scientist, “then you’re fine. But what are you _really_ doing here?”

 

Sans shook himself and his coat, a little, making sure no smaller parts were rattling around, anywhere. As he did, he said, “undyne had this stupid idea, just because she found out it’s my birthday. there was _no_ way i was just gonna go along with it, so i got outta there.”

 

Alphys smiled as she clapped her hands together. “It’s your birthday? _Tanjobi oumedetou!_ ”

 

Sans stopped shaking to stare at Alphys. “…huh?”

 

She was blushing miserably as she said, “Um… th-that’s how they s-say ‘happy birthday’ i-in anime.”

 

“oh… okay. thanks, al.” He smiled at her. It wasn’t surprising that Alphys didn’t know it was his birthday. He usually didn’t tell people, since it wasn’t all that important. But it brought up a good question. “wait, why did paps tell fish lips it was my birthday?”

 

Alphys shrugged uncertainly, unsure whether the question had been directed at her, or if it had been rhetorical. She didn’t get to find out because a loud, insistent knocking was visited upon the lab’s front door.

 

“Hey, nerd, open up! We need to talk!” _Bam, bam, bam, bam_ went Undyne’s fist, making Alphys worry about the door’s structural integrity.

 

As a comedian, Sans was offended. He shook his head with one brow ridge raised as he said, “worst knock-knock joke _ever_ . ” He shoved his hands into his coat pockets and started walking in the opposite direction, to the lab’s back door. “ welp, **time** out.”

 

Alphys tried to stop him, reaching a hand for him. “H-hey! You can’t j-just leave me here to deal with her, alone!”

 

Sans said, over his shoulder, “sorry, al. but i’d kinda like to stay in one piece ‘til my next birthday, yknow?”

 

His lizard friend’s hand fell as she said, “I see your point.” Undyne then burst into the room, but Sans was already long gone.

 

~~~~~***~~~~~***~~~~~***~~~~~

 

Back outside, Sans sighed. Was the fish stick going to chase him _all day_ , until she got her hands on him for that stupid human thing? Why did Papyrus have to sic her on him, this way? Then again, he probably didn’t know she’d be doing this sort of thing, so it was hardly his fault. He was probably just trying to do something nice. He would have to track Papyrus down and ask him. Come to think of it, he hadn’t seen his bro since breakfast. Granted, he hadn’t been back to the house in a while. Maybe that should be the first place to look? But before he could head that way, another familiar voice stopped him.

 

“Hello, Sans! What brings out here?”

 

He turned around, finding Toriel behind him. She was in her clinic uniform, and was carrying a box in her arms. “oh, hey tori. nothin’ much. just about to head home, actually.”

 

Toriel smiled. “I am going home, as well. I was asked to run an errand, and-” She stopped mid-sentence, focusing intently on Sans’ face.

 

It made him a little uncomfortable. “uh, do i have something on my face?”

 

“Yes, you do,” said the princess. “There is a small hairline fracture along your mandible, on the right side.” She grabbed him by the hand and started hauling him behind her. “You are coming to the clinic to have it treated.”

 

“aw, c’mon, tori! i’m fine!” Even as he said that, Sans touched his mandible and finally felt his injury. It was a tiny thing, so small he hadn’t even noticed it before she pointed it out, but it was there. It must have happened when he fell into that box of metal and plastic parts. It stung a bit…

 

Without looking behind herself, Toriel said, “I have heard that one before, Sans. I am still treating you.”

 

The time bug rolled his eyes. “ _fine_. but you don’t have to hold my hand! i can walk by myself.”

 

She didn’t let go. “If I release you, you will run away.”

 

Sans scoffed. “oh, _puh_ -lease! name one time.”

 

“Last Thursday. You were due for your booster shot and ran off before it could be administered. You have not visited the clinic, since.”

 

Sans blushed, having forgotten about that. “oh, right. heh! sorry, tori. i, uh, don’t like needles.” He had been dealing with the things all his life. Could he be blamed for not wanting any more stuck in him?

 

Toriel, still facing forward, didn’t notice any change in Sans’ expression. But she did say, “I am well aware of your discomfort with needles, Sans. But your health is of greater concern to me.” Her hand tightened on his. “So please, do not run away, again.”

 

He thought for a moment, then sighed as he said, “oh, alright.” She really was a good friend, even if she was a bit of a worrywart.

 

The treatment didn’t take long. Just a little healing magic to his mandible and he was good as new. But before he could leave, Toriel smiled brightly and said, “That is right! Sans, permit me to wish you a happy birthday.”

 

Stopping mid-stride, Sans stared at her. “how’d you know that was today?”

 

“I met your brother, while I was on my errand. He was the one to tell me.”

 

“he did, huh?” Just what was the little rascal up to? “anyway, thanks, tori.” He tried to leave again, but Toriel’s hand grabbing his wrist prevented that.

 

With a pleasant smile, she said, “I do believe there is still the matter of that booster shot to attend to.”

 

Sans was filled with dread. He tried wheedling his way out of things. “aww, but it’s my birthday! you can’t expect a guy to deal with that on his birthday, can you?”

 

Still smiling, Toriel said, “Had you received your shot when you were supposed to, we would not have to do it today.”

 

Sans couldn’t argue with that. He tried to pull his wrist away, but Toriel wasn’t making it easy. In fact, he knew she could drag him away to see the doctor, bag of tricks or not.

 

A chill wind blew through his bones. It looked like he was getting ticking shot, after all.

 

~~~~~***~~~~~***~~~~~***~~~~~

 

Sans rubbed at his chest, since he couldn’t rub his soul in public. That magic booster shot always _hurt!_ He didn’t even need it, but he got it every couple of years, anyway. Doc Gaster always said there was no harm in it, but Sans’ opinion differed on matter. Vehemently.

 

He sighed. Welp, what was done, was done. There was no point in wasting energy whining about it. He still had to find his little brother and ask him what the tick he thought he was doing, telling all their friends about his birthday. Though he seemed to have missed Alphys… that or Sans had run into her before Papyrus had the chance to tell her. Still, it raised the question of “where was he, now?”

 

Probably not at the castle. Prince Asgore Fluffybuns was _way_ too busy with royal stuff to entertain unannounced guests. Probably not Gorgette’s house, since they didn’t know where she lived (and Sans REALLY hoped Papyrus wasn’t going to tell her.) Of all their friends, that just left the Blook cousins and…

 

Just as he was thinking about them, Sans saw Frisk up ahead. They were reading a book while sitting under a tree, which gave him an idea.

 

A little sneaking and a little blue magic later ( _much_ easier than climbing), Sans was above Frisk, in the boughs of the tree. He started dropping handfuls of leaves on their head, confusing them for a little while before they thought to look up. Their face met more leaves, making Sans chuckle.

 

Frisk was smiling, too. “I guess it’d be asking too much for you to get down and **leaf** me alone?” they asked.

 

And so, the pun-off began. Sans retorted with, “why should i? trees are the best place **fo-rest**.”

 

“You don’t look very rested to me. You look **sap** ped of energy.”

 

Sans suddenly didn’t feel like playing, anymore. “ugh, don’t remind me.”

 

Frisk was concerned. “What’s wrong?”

 

Sans climbed down the old-fashioned way, sitting next to Frisk as he said, “undyne has this stupid idea about spanking me, just because it’s my birthday. she says it’s something humans do.” Incredulously, he asked, “do you seriously do that sorta thing?”

 

Frisk nodded, but also said, “They aren’t supposed to be real spanks, though. Just fake ones to embarrass you in front of your friends. But it doesn’t sound like Undyne knows that…”

 

Sans shuddered, rattling slightly. “pretty sure she doesn’t. and she’s already tracked me down twice.”

 

Frisk looked up, and in the general direction of the clinic. “I think she’s working on number three.”

 

Sans followed their squinty gaze, seeing the tall dust cloud that _somebody_ was leaving in their wake as they ran. Sans softly said, “no tickin’ way,” as Undyne became visible.

 

Frisk put a hand on his shoulder, saying, “Quick! Hide behind the tree. I’ve got an idea.” They stood and left the shade, making themselves more visible to Undyne as Sans hid. The royal guard-in-training arrived shortly afterward, skidding to a stop and making her dust cloud expand. Sans peeked around the tree as much as he dared to watch them while they talked.

 

Thankfully, Undyne hadn’t seen him before he hid. To Frisk, she said, “Hey, punk! Have you seen Sans, today?”

 

Frisk, coughing on the dust a bit, shook their head. “Can’t say I have. Why?”

 

Undyne reached into a pocket, pulling out some kind of piece of paper. “It’s the dweeb’s birthday, and Papyrus asked me to have our friends sign this.” She gave Frisk a pen, and the human signed whatever-it-was. Sans was curious, but Undyne wasn’t done.

 

“I’ve already seen Alphys and Toriel. I’m supposed to go see Asgore now. But if you see that bony coward, _stall him_. Papyrus doesn’t want him home before 4pm!”

 

“Okay. But one thing, first.” Undyne raised an eyebrow at them, just before Frisk said, “Since you don’t normally do stuff like this, does that make you a fish out of water?”

 

Sans had to hide completely behind the tree, covering his mouth as he struggled not to laugh. Undyne’s face had been _priceless!!_ But Frisk boldly went on.

 

“It’s odd that you would do anybody a favor. Are you feeling alright?”

 

Undyne spoke through clenched teeth. “I. Am fine. Thank you.”

 

“Are you sure? You’re looking a little… green around the gills.”

 

“SHUT UP!!!” Undyne glared at Frisk for a moment, but then…

 

“Whatever you say, **sturgeon** general.”

 

Undyne roared, and Frisk bolted while dodging spears like a pro. They led her away from Sans and the tree, and the skeleton finally let himself laugh out loud.

 

~~~~~***~~~~~***~~~~~***~~~~~

 

After recovering from his belly-laughing, Sans went home. It was a little after noon, and he was hoping to catch Papyrus in the middle of whatever-it-was he was doing.

 

Sans snuck in quietly, wanting to surprise his brother. But he wasn’t in the living room, or the dining room or kitchen, and everything _seemed_ normal. Maybe he was in his room? Or outside? But when Sans opened the door to Papyrus’ room, he was met by something unexpected.

 

Nothing. There was absolutely _nothing_ out of the ordinary. With no other leads, he went outside. Again, there was nothing to indicate anything was going on. Sans was left scratching his skull.

 

Was he too early? Was Papyrus off somewhere, gathering whatever supplies he needed for his plan? What did he think he could do, all by himself? Where was he?

 

* _…is he okay? he knows he should be home, by now. did something happen? what if-_

 

Sans’ thoughts were interrupted by a sound, coming from _his_ room. Papyrus didn’t normally go into his room…

 

He grit his teeth. _*_ _is it a burglar? i swear, if they did something to paps…!_

 

Sans ran up the stairs. He kicked opened the door, eyes glowing and ready to rumble. He startled the intruder, who was laying on his belly on the floor.

 

“NYEH?! BROTHER? YOU’RE HOME! I-I MEAN, DON’T LOOK! IT’S NOT DONE, YET!”

 

Papyrus was trying to cover up a large piece of paper with the upper half of his body. As relief flooded Sans’ body he looked around, finding all manner of things that he hadn’t had in his room, this morning. Colorful chains made with construction paper, ready to hang wherever, party hats and little party favors, rolls of streamers, the list went on.

 

Now calm, Sans asked, “paps, what’re you doing in my room?”

 

Busted, the little skeleton stood up, clutching his project in his hands. Hesitantly, he confessed.

 

“I KNOW I’M NOT SUPPOSED TO BE IN HERE, WITHOUT PERMISSION BUT… JUST IN CASE YOU CAME HOME EARLY, I WAS HOPING THIS’D BE THE LAST PLACE YOU’D THINK TO LOOK FOR ME! YOU KNOW, BECAUSE YOU ALWAYS SLEEP ON THE COUCH, FOR YOUR AFTERNOON NAP! AS FOR WHAT I’M DOING…” Papyrus turned the paper he was holding around, letting Sans see it. It was a half-colored drawing of the two of them and Doc Gaster, with all their friends surrounding them. Sans was in the middle of it all, with a big smile on his face. Papyrus continued while he looked it over.

 

“YOU’VE BEEN QUIET, LATELY. WELL, QUIET FOR _YOU_ , I MEAN. AND A LITTLE SAD, EVERY NOW AND THEN. I WANTED TO DO SOMETHING NICE, TO CHEER YOU UP, BECAUSE THAT’S WHAT COOL BROTHERS DO!”

 

Sans was a little stunned. “so… you’ve been planning a birthday party, for me?”

 

“YES!!” Papyrus grew more animated as he revealed everything. How he had enlisted Undyne to help everyone sign a special birthday card, and keep Sans from coming home too soon. How he had figured out Sans’ favorite cake flavor, and had asked Toriel to help him bake one up, later. How he was going to make all the decorations by himself, so everything would be _extra_ special! Toriel had said she’d help him hang them up, too. But now…

 

“EVERYTHING WAS SUPPOSED TO BE A SURPRISE! BUT NOW IT WON’T BE. I WAS HOPING UNDYNE WOULD KEEP YOU DISTRACTED, LONGER!”

 

Sans held back a laugh. “s-sorry, pap. she was the one that got distracted. she ran into frisk, and they tried out some puns on her. you know how she is with puns.”

 

Papyrus nodded. “EXACTLY! I THOUGHT SHE’D BE CHASING YOU AROUND FOR MOST OF THE DAY!”

 

Sans’ smile became a little fixed as he thought, _*so he DID sic undyne on me…_ Aloud he asked, “were you the one who told her about the human birthday tradition?”

 

Papyrus tilted his head. “WHAT TRADITION?”

 

“nothin’. forget i asked, buddy.” Sans pat his brother on the head, relieved that he was innocent of THAT much, at least. Still, he hadn’t realized his thinking about the future had been _that_ obvious. Had he really been that much of a mope about it? He didn’t mean to worry anybody, especially not his little brother. He might have to take his thinking someplace else, from now on…

 

Changing the subject, Sans said, “sorry about the surprise being spoiled. y’know, i could always _pretend_ to be surprised. i can be pretty convincing, look!” Sans feigned surprise, knowing full well it wasn’t very convincing, but giving it a shot, anyway. Papyrus wasn’t amused.

 

“THAT DOESN’T COUNT!” He pouted up at his big brother, looking adorable despite his frustration.

 

“heh! sorry, pal.” Even as he chuckled, Sans did feel a little bit bad. Papyrus had clearly been working hard on this surprise. It was a shame he hadn’t managed to pull it off. But running around today, seeing all his best friends, having a laugh or two… All-in-all, it had been a pretty good birthday (minus that shot but hey, a guy couldn’t have everything. At least Toriel had meant well.)

 

It all made Sans think, _*i’m a pretty lucky guy, aren’t i?_

 

The older brother smiled. “hey, paps. you wanna know somethin’?” When the younger brother nodded Sans knelt down, meeting his eyes. “you did manage to surprise me with one thing. you reminded me of how many cool friends we’ve got. and how i’ve got the coolest little bro in the world.”

 

Papyrus was beaming. “REALLY??” At Sans’ nod the brothers embraced, though the elder added a bit of a noogie for the whole Undyne thing. But he was laughing as his brother tried to wriggle away from him.

 

Just for today, the future could wait. All those timelines, all those possibilities, Fate… they could wait, too. Right now, metaphorically surrounded by his friends and family, Sans’ present was looking pretty sweet.

* * *

  
  



End file.
